Not Applicable
Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates in general to optical 4-port couplers and relates in particular to 4-port couplers operating as splitters and combiners.
2. Discussion of Related Art
4-port couplers are commonly used integrated optic devices. 4-port couplers are typically used for splitting a signal into two signals of half power and can also be used to combine two signals, producing one or two output signals. A 4-port coupler that produces phase dependent output signals is used as a combiner and splitter in a coupler-based programmable phase logic device, which is disclosed in U.S. patent application Ser. No. (Attorney Docket No. 2000-004), assigned to the assignee of this application.
Integrated optic 4-port couplers are also known as directional couplers, are symmetric devices with no unique physical orientation, and are described by coupled mode analysis. The interaction between two input signals, and the resulting output signals, is partially described by a coupling coefficient. In coupled mode analysis, the coupling coefficient or the complex conjugate of the coupling coefficient can be used to describe signal interaction. However, this results in a physical ambiguity because the arbitrary choice of the coupling coefficient or the complex conjugate of the coupling coefficient affects the input and output phase values. According to coupled mode analysis, an input signal directed into the first input port of a 4-port coupler operating as a signal splitter will produce output signals with different phase values from the output signals generated by the same input signal directed into the second input port of the 4-port coupler. Therefore, coupled mode analysis indicates that the 4-port coupler has a phase dependent orientation, even though the 4-port coupler has no unique physical or manufacturable orientation. This ambiguity increases the difficulty for producing consistent phase dependent circuits using 4-port couplers.
It is, therefore, an object of the present invention to provide a 4-port coupler that is not ambiguous in design and produces predictable phase dependent splitting and combining operation results.
The phase dependent splitter/combiner 4-port coupler device employs two amplifiers, two splitters, a phase inverter, and two combiners. The 4-port coupler device produces two output signals with predictable phase values from given input signals.
The 4-port coupler device receives two input signals and is composed of two duplicating stages and a cross-over stage. Each duplicating stage receives one input signal, consists of one of the amplifiers and one of the splitters, and produces two duplicated signals. The cross-over stage receives the four duplicated signals from the two duplicating stages, consists of the phase inverter and the two combiners, and produces the two output signals.
The 4-port coupler device receives the two input signals, that are preferably either equal in phase or opposite in phase, and produces the two output signals. In the duplicating stages, the two input signals are preferably doubled by the amplifiers and then split to produce the four duplicated signals. The four duplicated signals are intermixed so that the first duplicated signal is combined with the third duplicated signal in a first combiner and a phase inverter inverts the phase of the second duplicated signal before it is combined with the fourth duplicated signal in a second combiner.
The device has a well-defined phase dependent operation that can be designed for a particular set of output signals by the placement of one or more phase inverters.
Two types of combiners that can be used in the cross-over stage are 3 dB couplers and non-3 dB couplers. If the combiners are 3 dB couplers and only one 4-port coupler device input signal is present, the 4-port coupler device performs a splitter operation and the input signal is preferably split between the two output signals. An input signal directed into the first input port of the 4-port coupler device will produce a first output signal that is half the intensity of, and equal in phase to, the input signal and a second output signal that is half the intensity of, and opposite in phase to, the input signal. An input signal directed into the second input port of the 4-port coupler device will produce two output signals that are half the intensity of, and equal in phase to, the input signal.
If the combiners are 3 dB couplers and two input signals are present, the 4-port coupler device performs a combiner operation. When two 4-port coupler device input signals are present, the first output signal of the 4-port coupler device is the phase dependent sum or partial sum of the input signals and the second output signal of the 4-port coupler device is the phase dependent difference or partial difference between the second input signal and first input signal.
If the combiners are non-3 dB couplers and only one 4-port coupler device input signal is present, the 4-port coupler device performs a replicator operation, providing two output signals that are preferably equal in intensity to the input signal. An input signal directed into the first input port of the 4-port coupler device will produce a first output signal that is equal in intensity and phase to the input signal and a second output signal that is equal in intensity, and opposite in phase, to the input signal. An input signal directed into the second input port of the 4-port coupler device will produce two output signals that are equal in intensity and phase to the input signal.
If the combiners are non-3 dB couplers and two 4-port coupler device input signals are present, the 4-port coupler device performs a combiner operation. If two 4-port coupler device input signals are present, the first output signal of the 4-port coupler device is preferably the phase dependent sum of the input signals and the second output signal of the 4-port coupler device is preferably the phase dependent difference between the second input signal and first input signal.
The device can be used for optic, including infrared and ultraviolet, or microwave signals.